Methods and apparatus for dry cleaning



Aug. 16, 1960 E. B. MICHAELS El'AL 2,949,336

METHODS AND APPARATUS FOR DRY CLEANING' Filed May 28, 1956 RESISTZM/GE $EN$ITIVE RELAY 50L E N010 5 WASHER BUTTON TRAP IN VEN TORS. EDWIN B.M/0HAEL$, MORE/5 U. COHEN,

United States METHODS AND APPARATUS FOR DRY CLEANING Filed May 28, 1956, Ser. No. 587,620

7 Claims. (Cl. 8-142) The present invention relates to methods and apparatus for dry cleaning fabrics, garments and the like without injury thereto. More particularly, it relates to processes of the type which are carried out by the careful regulation of water absorption by garments to be dry cleaned by the control of relative humidity within a washer. Still more particularly, the invention is directed to methods for the utilization of a sensing element, more particularly defined hereinafter, for relative humidity determination directly placed in the dry cleaning solvent.

The term relative humidity (R.H.) within the solvent or garment as used in this specification may be defined as the ratio of the vapor pressure of water in the solvent or garment to the vapor pressure of pure water at the same temperature as that of the solvent or garment. As is customary, the degree or value of relative humidity is expressed as percent R.H. In this description R.H. values in the solvent above about 80% may be defined as free water and R.H. values below about 80% may be defined as bound water.

In the dry cleaning of fabrics and garments forthe removal of ground-in soils and sweet stains, it is known that the amount of moisture pick-up by such fabrics or garments as determined by the relative humidity within the cleaning solvent plays a very considerable effect in removing various types of soils and stains. For example, too little water will remove little, if any, soil. Excessive moisture Will also deleteriously efifect garments or fabrics in the form of possible shrinkage, wrinkling and color loss. Usually, for best overall results, the relative humidity within both the solvent and garment has been maintained at from about 60% to about 80%. The relative humidity within a dry cleaning system may be altered by varying the free water content in the washing Zone. For instance, water may be prevented from entering that zone. Conversely, if it were desired to increase the relative humidity of the cleaning system, entry of water is permitted. As a practical matter, it has been demonstrated previously that solvent relative humidity and garment moisture pick-up must be accurately established and maintained. Otherwise, the efficiency of the cleaning operation for purposes of removing soils, stains and like is markedly low. To the present, such control, if possible, has been singularly diflicult to attain.

In the past, many proposals have been suggested for controlling relative humidity within a dry cleaning washing zone. Unfortunately, each has had its short-comings. One procedure suggested was to precondition soiled garments to a known moisture content and then add them to a cleaning solvent of some controlled moisture value. At best this procedure will give only an approximation of the solvent relative humidity due to the difficulties in preconditioning garments to predetermined uniform low relative humidities. Further, such garment drying technique is not commercially feasible.

A drying operation is both costly and impractical, since atent "ice many stains are set by heat and are rendered exceedingly more difiicult to remove, if at all.

Another method recently developed for dry cleaning is the use of humidity gages to measure the relative humidity of the air above the cleaning solvent in the dry cleaning washer. This procedure utilizes the principle of passing a stream of air from the washer over a humidity sensor or sensing element fixed in a gage housing at a point above the solvent. Again, such a procedure does not adequately control both the solvent and garment relative humidities without the constant attention of the dry cleaning operator. Even where such attention is given, nevertheless there remains inherently a hiatus in sensing element response between changes in relative humidity of solvent and relative humidity of the air above the solvent. Also, for example, if a hair hygrometer or other animal membrane hygrometer is used, such sensors respond to a bulk moisture efiect onthe membrane or hair. The response will show hysteresis values which makesuch measurements ineifectuaL' Accordingly, this general procedure does not lend itself to commercial exploitation.

A still further method whichhas been suggested for controlling solvent R.H. is to measure the conductivity of the dry cleaning solvent. However, such measurements are not entirely accurate, for the reason that the introduction of water into the washing zone cannot be readily measured by conductivity. This may be explained by the fact that water may affect the conductivity of many solvent-detergent cleaning mixtures in different ways. For example the conductivity of the solvent may increase in a linear manner as water is first added to the system. This increase in conductivity is linear only until the free water level (about R.H.) is reached. However, above this level, the R.H./conductivity curve which at low moisture content proceeded in a linear fashion usually inverts to show a maxima above 80% R.H., the conductivity actually decreasing with added moisture. Thus, when water is added to a cleaning system, conductivity measurements of the solvent are usually unreliable because beyond an R.H. of about 80% the conductivity reading may actually indicate an R.H. less than 80% due to the aforementioned inversion phenomenon. Therefore, when garments are being subjected to large amounts of water, the conductivity reading may be interpreted as showing an R.H. value below 80%, although the garments are being irrevocably injured. This situation can be compensated for .by providing smaller additions of water to thereby regulate the conductivity of the solvent such that the R.H. is not permitted to exceed 80% at any time either before garment addition or during washing. However, such amounts of water can be present in the cleaning system as bound or less available water, physically bound to the solvent-detergent mixture. Moisture in the cleaning zone is therefore limited both by the quantity of water which a particular solvent/detergent system can dissolve at activities below 80% as well as by the physical state of that water. As such, this cleaning system cannot supply the requisite quantity of water at a rate to affect the surface of the garment for purposes ofefficient removal of soils and sweet stains. Accordingly, conductivity measurements of solvents for purposes of determining R.H. are unreliable and inefiectual in modern dry cleaning operations which employ solvent/ detergent cleaning solutions. a

Expenditures of money, time andeifort have been spent to provide accurate methods for controlling R.H. in a Washer unit. To the present all such previouslydisclosed metho'ds have fallen short of their goal.

A principal object of the invention, therefore, is to of solvent RH. and garment RH. directly in the washing chamber without resort to the determination of the moisture content either in the air above the solvent or in the solvent prior to its entry into the Washing chamber. These and other objectsare accomplished in a simple and straightforward manner.

Briefly, accurate control of water addition both to soiled garments and to a commercial cleaning solution comprising a detergent charged organic solvent, can be attained by the provision of a detergent activated, chemically surface modified dielectric sensing element placed directly in the washing zone. In this manner, the sensing element actsas an analogue of the garment surface so as to indicate its R.H. status and to predict the terminal R.H. of the garment under a constant rate of moisture addition.

We have unexpectedly discovered that an inert, integral and ionic modified-surface dielectric element acts accurately as a senso'r in a detergent charged hydrophobic solvent when placed directly in a washer or washing Zone. This is unexpected because such sensing elements are generally worthless or at best inefiective in a hydrophobic environment. Therefore, according to the process of the present invention, an inert, integral, modifiedsurface sensing element when placed in a washing zone so as to regulate RH. within that zone, will readily and quickly detect R.H. changes therein so as to permit eflicient cleaning of garments within shortened time periods. It is an important advantage of the invention that a safe and efficient dry cleaning method is. for the first time attained in shortened time periods. Without limiting the invention to any particular theory, our novel method, may be explained by the fact, that water, which is essential in modern dry cleaning operations, can be introduced rapidly into the washer at a regulated rate so as to attain a desired relative humidity range Within the washer for effecting safe dry cleaning and insuring a safe terminal R.H. of the garments. However, since the rate of water addition is rapid, the detergent charged solvent cannot apparently bind all of the introduced water, the solvent thereby becoming saturated. Only a portion of the introduced water may be bound to the solvent detergent mixture and the remainder is available as free water to effect cleaning of the garments. The importance of a suitable sensing element comes into prominence in detecting free water and in determining ho'w the available free or unbound Water is affecting the garments during the cleaning operation. The use of our element whose moisture response is a surface effect gives a true recording of the free moisture effect on the garments surfaces. It appears that the sensing surface response to the moisture level in the Washer is analogous to the garment surface. Moisture introduced into the system at a constant rate raises the bulk moisture content of the garments. 'Our surface sensor predicts the state of the surface of the garment by responding to the excess available moisture in the washing zone. This excess develops due to lower rates of absorption by the garments at higher moisture levels. The sensing element responds more rapidly than does the garments, thus preventing the introduction of excessive quantities of water.

Necessity in our process for recleaning of only insignificant percentages of the garments evidences the eificiency of the sensor in its ability to register the RH.

exposure to the surface chemical modifiers.

4 status of the cleaning system, particularly with reference to the terminal R.H. of the garment.

Any of a large variety of dielectric sensing elements may be used in the process of the present invention provided the elements areinert in the cleaning solvent and characterized by their ionically modified surfaces. Further, they may be also defined byresistance characteristics. In general, the use of elements which record resistances o'fbetween about 0.02 megohm per square of sensing surface and about 100 megohms per square of sensing surface as determined in an organic cleaning solvent of 75 R.H. is particularly advantageous.

A sensing element may be prepared from a variety of organic materials. Illustrative of the latter are waterinsoluble solid resins or polymers such as for example, the epoxy resins, polyethylene, polypropylene, copolymers of polystyrene, polyesters, urea-formaldehyde, melamine-formaldehyde, cellulose esters and ethers, and phenol-formaldehyde resins. The surfaces can be chemically modified to an ion-ative state as by sulfonation, carboxylationor pho'sphonylation. The electrical resistance of the surface will vary according to the degree of For example, it has been found that the longer the chemical treatment, the lower the resistance of the element, and conversely, the shorter the treatment, the higher the resistance. The element is then exposed to a surface active reagent, such as petroleum sulfonate, 'to activate the element for purposes of moisture response in hydropholic solvents. Alternatively, activation of the element can be accomplished in situ by insertion of the surface modified element into a charged solvent system. Of all the sensing elements above mentioned, surface sulfonated epoxy resins are especially well adapted for use as a humidity sensing element.

The preparation of various sensing elements is given by way of illustration in the following examples and such examples are not intended to be taken as limitations upon the invention. Where Stoddard solvent is used in this description, it means a colorless refined petroleum solvent having a boiling point range between l54.4 C. and 202.2 C.

Exampie A To 60 grams of Shells Epon 828 (a diglycidyl ether of bisphenol which is a viscous liquid at room temperature having a viscosity of 5000-11000 cps. and an epoxide equivalent of 175-210) is added 3 grams or" diethylenetriamine and stirred at room temperature until a clear solution is obtained. The clear solution thus treated is poured on an inert stainless steel plate and the cast solution is cured at C. for eighteen (18) hours. The cured epoxy resin is 'next stripped from the stainless steel plate and cut into one half inch squares. Each square is sulfonated by incorporating the latter in a mixture of one gram of. chlorsulfonic acid and 160 grams of anhydrous carbon tetrachloride at 70 F. for about two minutes. The so sulfonated resin is immersed in diethyl ether and rinsed several times with additional diethyl ether. It is then dried and rinsed with distilled Water't-o removeexcess acid. The resin is neutralized with a 5% aqueous sodium carbonate solution. Excess sodium carbonate is then removed with water and electrodes'are attached to a thus treated epoxy resin surface and the resistance is measured by usual methods using A.C. currents. The resistance registers one megohm per square at 75% relative humidity and 0.5 megohrnp'er 's'quare'at a relative humidity of when placed in a solution of perchloroethylene containing 4% petroleum sulfonate.

ExantpleB A'cure'd phenol-formaldehyde resin ofv one-half inch squares is 'sulf'onated following the procedure of Example A in every material detail. The element which shows that its surface was sulfonated possesses in the solventdetergent medium of Example A an electrical resistance of 0.5 megohm per square at 75% relative humidity and 0.17 megohm square at 85% relative humidity.

Example C A cured mica-modified phenol formaldehyde resin is prepared in two strips of one inch squares. These are sulfonated in fuming sulfuric acid for 2 minutes at 80 C. The surface-sulfonated element is next immersed in diethyl ether, removed and rinsed several times in the latter solvent to remove any residual acid. The elements are rinsed in water and neutralized with dilute aqueous sodium carbonate and excess carbonate is removed with water. The element is then immersed in a 1% solution of petroleum sulfonate in Stoddards solvent at.40 C. for 24 hours. Electrodes are attached to the so-activated element and its resistance is measured in Stoddard sol-. vent. It is found that the electrical resistance at R.H. 75% is 0J6 megohm per square and 0.2 megohm per square at 85%. -A cross-linked polystyrene resin can be substituted for the phenol-formaldehyde resin above. Similar properties are obtained.

Example D Polyethylene square of three-quarters inch is sulfonated in a mixture comprising one gram of chlorosulfonic acid, 160 grams carbon tetrachloride and 20 grams of dioxane for 76 hours at 20 C. After sulfonation, the resin is Washed first with ether and then with Water to remove residual acid. To insure complete acid removal, the washed resin is treated with a dilute aqueous potassium carbonate solution followed by treatment with water. When the element is exposed to the detergent charged solvent of Example C, its resistance is determined as at 2.7 megohms per square at relative humidity of 80%.

Example E A strip of commercially available cellulose acetate is partially deplasticized by extracting the latter in perchloroethylene solvent. Resulting deplasticized cellulose acetate is then immersed at 70 F. in 50% aqueous monoethanolamine for one hour. It is then washed to remove the monoethanolamine. The so treated resin is next wetted with monochloroacetic acid and air dried over night in the presence of said chloroacetic acid solution. The surface carboxylated resin is next immersed in 50% sodium hydroxide at 30 C. for 40 minutes. The resin is neutralized in acetic acid and the latter removed by washing in sodium chloride solution and, finally, the surface modified resin is Washed with Water. The element is immersed in a detergent charged solvent as in Example C. It shows a resistance of 2.8 megohms per square at 75 R.H. and 0.25 megohm per square at R.H. of 85%.

Substituting phosphoric acid for the chloroacetic acid employed above will result in a phosphonylated surface modified resin showing similar properties as obtained in this example.

The sensing elements prepared in accordance with the procedures set forth above may be removably mounted on an inert plug adapted to be inserted into a washing chamber. The plug will contain a pair of electrical terminals, which are in direct contact with the sensing element surface. The sensing element may be pressure fitted to electrical contacts of the plug.

The invention will be further described with reference to the accompanying drawing, the single figure of which is a fiow sheet which constitutes one mode for practicing the invention. Thus, a dry cleaning plant embodying the principal features described above is diagrammatically illustrated below.

Referring now to the drawing, a washing chamber is generally designated at 1. Filtered solvent is fed through line 2 and then through an opening 3 into the washing chamber. A sensing element 4, such as prepared in Example A, above, is mounted on a plug 5. The plug is removably attachable to the washing chamber by providing matching threads (not shown) on the plug and in the opening of the washing chamber. The sensing element is linked to a resistance sensitive relay 6 through wires in cable 7 attached also to plug 5. A relay 6 then actuates solenoid valve 8 through wires 7a when the resistance of the element is above the controlling value. Thus water introduced into the solenoid valve through line 9 will flow through line 9a into line 2. By spraying the water into linej2 as at nozzle '10, intimate mixing with solvent will occur readily. In the interim, solvent in the washing chamber is withdrawn through a button trap 12 by means of pump 13 and fed through filter 14. Solvent is next returned to the washing zone 1 through line 2.

The following examples for controlling the amount of moisture addition to a cleaning system are presented to facilitate a better understanding of the invention. It will be noted that the R.H. of. the garment phase will not exceed although the R.H. of both the solvent and garments are not necessarily the same at the same time.

Example 1 To a dry cleaning washer unit of 30 pounds capacity as in Figure 1, is added 30 gallons of perchloroethylene solvent which circulates at a rate of 30 gallons per minute between the filter and washer during the washing cycle. Since the R.H. of the cleaning system' is less than 60%, Water is injected into the solvent line entering the washer at the rate of 6 oz. per minute. The solvent is charged with 4% by volume of a commercial (petroleum sulphonate) detergent. A 4% solution of this detergent in perchlorethylene will normally register a R.H. equivalent of 75 with about 0.15% total water and will not dissolve more than 0.2-0.4% water dependent upon temperature and impurities. Since 6 oz. of water per 30 gallons of solvent is equal to 0.15% water by volume, this 75% R.H. value is therefore exceeded by the incoming solvent.

The washer is provided with an epoxy sensing element as prepared in Example A above. This element possesses a resistance of 0.2 megohm when in equilibrium with the detergent charged solvent containing a moisture equivalent of 75 R.H., but in air the element will have a resistance of 2.0 megohms at a R.H. of 75%.

The cleaning cycle comprises a wash cycle of 15 minutes and extraction cycles of two minutes before and after a rinse cycle of three minutes. After which time the garments are removed for drying and deodorization.

30 pounds of mixed woolens are introduced into the above described washer. The pump fills the washing zone with solvent. This is circulated during the 15 minute washing cycle. Moisture is allowed to enter-the solvent up to 0.8 megohm resistance of the aforementioned sensing element. The R.H. of the garments before introduction into the washer was measured and determined to have a regain value equivalent to a R.H. of 40%. The solenoid is activated by the relay to allow water to be injected and after three minutes the resistance of the sensor decreased from an original resistance in the solvent of 3 megohms to 0.8 megohm or 60% R.H. at which point the relay is regulated to shut off the water supply. Thereafter, for the next twelve minutes water intake is regulated to maintain a resistance of 0.8 megohm. Total water added to the cleaning system is 30 ozs. A terminal regain or water pick-up of the garments equivalent to a R.H. of 65% is attained. Examination of the garments after rinsing and extraction indicated that the garments showed no wrinkling of linings and complete removal of all surface stains.

Example 2 Controlled Moisture Time in Min. Water Addition on. 3- 013. 4- on.

Within 6 minutes, the controlled addition of water is terminated by a timer and washing cycle is completed; The total water added is 30 ozs. and terminal regain of the garments is equivalent to 70% RH. Excellent cleaning of soil and stains is attained.

Example 3 In this example, an 85 pound petroleum solvent washer which contains approximately 60 gallons of solvent during washing cycle and having a flow of solvent through the washer of 55 gallons per minute is used. Water is injected into the solvent line at the rate of 8 oz. per minute. Commercial grade solvent-soluble, dry cleaning detergent containing a mixture of petroleum sulfonates and polyethylene oxides of nonylphenol having an average molecular weight of 400 is added to the solvent to supply a concentration therein. A load of 85 pounds of silk dresses are added to the washer which operated during a normal cleaning cycle of 30 minutes followed by extraction cycles of 3 minutes before and after a 3 minute rinse. A sensing element comprising a sulfonated crosslinked polystyrene as prepared in Example C above having a resistance of 0.3 megohrn at 70% RH. equivalent solvent is inserted into the washing zone before washing commences. Moisture is added into the solvent feed. It is terminated when a resistance of 0.5 megohm is attained. However, the moisture control is operated for merely 15 minutes of the normal 30 minute cleaning cycle for excellent cleaning results. In this run, the quality of the cleaning was so high that 5% of the load required recleaning whereas the usual practice using a 30 minute cleaning cycle is to reclean 20% of the load or more.

The original moisture content of the silks was equivalent to a 40% regain but terminal regain at the end' of the cleaning cycle is 73%. The following sequence of moisture addition was recorded as. shown in the table below:

A 450 pound washer containing 300' gallons of Stoddards solvent and charged to 1 /2 of a commercial mixture of anionic, nonionic and cationic detergent. Water is introduced directly into the washer at the rate of 45 oz. per-minute= This washer was provided with an epoxy resin sensor prepared in accordancewithv Example A above which has a resistance of 1.5 megoh'mszit a solvent relative. humidity of 75% RH. and a resistance of 0.25megohm at a solvent relativehumidity of 85% RH. The addition of water is set so as to terminate. at 0.3 megohm resistance or about RH.

A load of 400 pounds of woolen pants at a R.H. of 25% initial regain is introduced to the washer containing 300 gallons of solvent without circulating solvent through the washer. The washer was run for 15 minutes in accordance. with the following schedule:

Total Controlled Moisture Time in Minutes Water Water Addition Added,

0-9. on 9-11 on 585 11-15 on Although the RH. of the solvent is set for 80% total regain of the garments in term-s of RLH. is 70%. This is due to the interchange rate of this type of washer and the control sequence is set to compensate for different type washers. Substantial complete washing is attained;

A large variety of solvents may be employed for example, Stoddards solvent; carbon tetrachloride, trichloroethylene and perchloroethyleneare in common use. Of these, perhaps Stoddards solvent is used most prevalently. However, perchloroethylene is rapidly gaining in popularity because of its non-flammable characteristics. Nonetheless, any of the solvents enumerated above may be used in the process of the invention.

The detergents which are used in conjunction with the solvents listed above are the anionic detergents, such as the petroleum sulfonates or non-ionicssuch as the alkyl aryl polyglycol ethers and alkylol amides or mixtures of both as exemplified herein. Any of the commercially available detergents can be used. Of these, the petroleum sulfonates are preferred.

The amount of detergent agent may be varied widely but in general from about 0.25% to 10% by weight of the solvent yields satisfactory results. However, larger or smaller proportions may be used.

We claim:

1. A process for enhancing the dry cleaning of gar ments andfabrics by the regulation and control of water added to a detergent charged organic cleaning solvent system which comprises introducing soiled garments into a washing zone, subjecting said garments to the washing action of an organic cleaning solvent containing detergent while introducing water therein; regulating the incorporation of water in said solvent system soas to establish and maintain a predetermined terminal RH. of the garments in the solvent cleaning zone of from about 60% to 80% and maintaining said predetermined relative humidity by incorporating a water sensing responsive device directly therein, said responsive device comprising an inert, integral, ionic-modified-surface dielectric synthetic resinmaterial.

2. A process according to claim 1 in which the inert, integral modified-surface dielectric material is a surface sulfonated epoxy resin characterized by an electrical resistance of one rnegohm per square at 75% relative humidity.

3. A process according to claim 1 in which the inert, integral, ionic modified-surface dielectric material is a sul+ fonated polyethylene resin characterized by a resistance of one megohm per square at 75 EH.

4. A process according to claim 1 in which a solventsoluble detergent-in the range-of from 0.25% to 10% is added to the solvent.

5. A, process according to claim 1 in which the solvent is Stoddards solvent.

6. A process according to claim 1 in which thesolvent is perchlorethyl'ene.

7. A process for enhancing the efiiciency of the drycleaning of garments and fabrics which comprises subjecting the latter to the washing action of a solvent detergent mixture in a washing zone incorporating a water sensing responsive device in said washing zone, adding water thereto at a rate so as to attain a R.H. of at least about 60% but not to exceed a R.H. greater than about 80% of the terminal R.H. of the garments, interrupting the supply of water but adding additional water when needed to attain said R.H. level, drying and deodorizing the so washed garments, said water sensing responsive element comprising a detergent-activated, inert, integral, ionic surface-modified dielectric synthetic resin material.

References Cited in the file of this patent UNITED STATES PATENTS Dorner Jan. 6, 1931 Reddish May 30, 1933 Hatfield Mar. 7, 1939 Dunmore June 9, 1942 Grimes July 5, 1949 Blodgett Jan. 10, 1950 Dannenberg June 23, 1953 Reeder et al June 8, 1954 Creighton et al June 22, 1954 Fulton Aug. 23, 1955 

1. A PROCESS FOR ENHANCING THE DRY CLEANING OF GARMENTS AND FABRICS BY THE REGULATION AND CONTROL OF WATER ADDED TO A DETERGENT CHARGED ORGANIC CLEANING SOLVENT SYSTEM WHICH COMPRISES INTRODUCING SOILED GARMENTS INTO A WASHING ZONE, SUBJECTING SAID GARMENTS TO THE WASHING ACTION OF AN ORGANIC CLEANING SOLVENT CONTAINING DETERGENT WHILE INTRODUCING WATER THEREIN, REGULATING THE INCORPORATION OF WATER IN SAID SOLVENT SYSTEM SO AS TO ESTABLISH AND MAINTAIN A PREDETERMINED TERMINAL R.H. OF THE GARMENTS IN THE SOLVENT CLEANING ZONE OF FROM ABOUT 60% TO 80% AND MAINTAINING SAID PREDETERMINED RELATIVE HUMIDITY BY INCORPORATING A WATER SENSING RESPONSIVE DEVICE DIRECTLY THEREIN, SAID RESPONSIVE DEVICE COMPRISING AN INERT, INTEGRAL, IONIC-MODIFIED-SURFACE DIELECTRIC SYNTHETIC RESIN MATERIAL. 